Thymosin beta(4) serves as a glutaminyl substrate of transglutaminase. Labeling with fluorescent dansylcadaverine does not abolish interaction with G-actin.

Thymosin beta(4) possesses actin-sequestering activity and, like transglutaminases, is supposed to be involved in cellular events like angiogenesis, blood coagulation, apoptosis and wound healing. Thymosin beta(4) serves as a specific glutaminyl substrate for transglutaminase and can be fluorescently labeled with dansylcadaverine. Two (Gln-23 and Gln-36) of the three glutamine residues were mainly involved in the transglutaminase reaction, while the third glutaminyl residue (Gln-39) was derivatized with a low efficiency. Labeled derivatives were able to inhibit polymerization of G-actin and could be cross-linked to G-actin by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. Fluorescently labeled thymosin beta(4) may serve as a useful tool for further investigations in cell biology. Thymosin beta(4) could provide a specific glutaminyl substrate for transglutaminase in vivo, because of the fast reaction observed in vitro occurring at thymosin beta(4) concentrations which are found inside cells. Taking these data together, it is tempting to speculate that thymosin beta(4) may serve as a glutaminyl substrate for transglutaminases in vivo and play an important role in transglutaminase-related processes.